Gas curtains, metal wire mesh, tape or chain curtains, and Refrasil® or other refractory materials are used in continuous furnaces. If the curtain is installed at the charge end opening and discharge end opening, it significantly contributes to reduce air ingress into the furnace, reduce protective atmosphere flow rate and reduce heat losses through the charge and discharge end openings. If the curtain is installed at the beginning of the cooling zone (or in the intermediary zone or at the end of the hot zone), it significantly contributes to reduce heat losses from the hot zone into the cooling zone, separates the atmosphere of the hot zone from that in the cooling zone (which require a higher H2/H20 ratio at lower temperature to protect against oxidation of metals) and permits a higher cooling rate, shortening the cooling time and the cycle time. In the case of austenitic stainless steels and other materials, cooling from the annealing temperature must be rapid, no more than approximately 3 minutes in cooling from 1600° F. to 800° F. If cooling (zone) does not provide a cooling rate sufficient to prevent carbide precipitation, maximum corrosion resistance will not be obtained.
In the case of the muffled continuous furnaces (including humpback furnaces) installation of the curtain at the beginning of the water cooling zones is very difficult if not impossible. It is therefore desirable in the art for a gas curtain assembly that can be easily inserted into the cooling zone from the discharge end.